1. Field of the Invention
This invention relates to a motion detection circuit for detecting motion in a video signal and a noise suppression circuit including the motion detection circuit.
2. Description of the Prior Art
A motion detection circuit for detecting motion in a video signal from a difference signal between the video signal and one-frame delayed video signal is known and a noise suppression circuit is also known. The noise suppression circuit includes the motion detection circuit, a circulation signal generation circuit for generating a circulation signal in accordance with the difference signal and the motion detection signal, and a subtractor for subtracting the circular signal from the video signal to output a noise suppressed video signal. Such a prior art motion detection circuit and a prior art noise suppression circuit are disclosed in Japanese patent application provisional publication No. 9-81754.
FIG. 9 is a block diagram of such a prior art noise suppression circuit including a prior art motion detection circuit.
The prior art motion detection circuit includes a frame memory 610 for generating a delayed video signal from the noise suppressed video signal Vo, a subtractor 602 for generating a difference signal (interframe difference signal) between the video signal Vi and the delayed video signal, a motion detection circuit 603 for detecting a motion from the video signal Vi and the delayed video signal to output a motion detection signal.
The noise suppression circuit further includes a subtractor 607 for generating the difference signal between the video signal Vi and the delayed video signal, a circulation amount determining circuit 608 for generating a circulation signal from the difference signal in accordance with the motion detection signal, and a subtractor 609 for obtaining a difference between the video signal Vi and the circulation signal to output a noise suppressed video signal Vo.
The aim of the present invention is to provide a superior motion detection circuit and a superior noise suppression circuit.
According to this invention there is provided a motion detection circuit. A delay generates a delayed video signal from a video signal including a luminance signal and a carrier color signal. The delayed video signal is delayed by one frame from the video signal. An interframe difference signal generation circuit generates an interframe difference signal from the video signal and the delayed video signal. A filter filters the interframe difference signal to remove the carrier color signal to output the interframe difference luminance signal. A first motion judging circuit judges whether an image at a target pixel in the video signal is moving from the interframe difference luminance signal to output a first motion judging result. A second motion judging circuit judges whether the image is moving from the interframe difference signal to output a second motion judging result. A third motion judging circuit judges whether the image is moving by combining the first motion judging result with the second motion judging result to output a judging result.
The motion detection circuit may further include an edge detection signal generation circuit for detecting an edge at the target pixel in the video signal and detecting an edge at the target pixel in the delayed video signal and outputting an edge detection signal from either of the detected edge in the video signal or the detected edge in the delayed video signal selected in accordance with a selection signal. The first motion judging circuit judges whether the image is moving from the interframe difference luminance signal at a pixel area around the target pixel. A size of the pixel area is controlled in accordance with the edge detection signal.
The motion detection circuit may further include an edge detection signal generation circuit for detecting an edge at the target pixel in the video signal and detecting an edge at the target pixel in the delayed video signal and outputting an edge detection signal from either of the detected edge in the video signal or the detected edge in the delayed video signal selected in accordance with a selection signal. The second motion judging circuit judges whether the image is moving in accordance with the interframe difference signal at a pixel area around the target pixel. A size of the pixel area is controlled in accordance with the edge detection signal.
In the motion detection circuit, the third motion judging circuit includes a logical operation circuit for effecting logical operation between the first motion judging result from the first motion judging circuit and the second motion judging result from the second motion judging circuit such that, except when the first and second motion judging results agree with each other in a moving condition and a still condition. The logical operation result is biased toward the moving condition.
In the motion detection circuit, the first motion detection circuit judges whether the image is moving with (J-1) threshold values to output J-valued the first motion judging result. J is a natural number more than one.
In the motion detection circuit, the second motion detection circuit judges whether the image is moving with (J-1) threshold values to output J-valued the second motion judging result. J is a natural number more than one. The second motion detection circuit further includes an interline interpolation circuit for interpolating the J-valued second motion judging result such that the J-valued second motion judging result at the target pixel is changed to the moving condition when the J-valued second motion judging result at the corresponding pixel on at least one of adjacent lines is judged to be the moving condition and horizontal interpolation circuit for interpolating the J-valued second motion judging result such that the J-valued second motion judging result at the target pixel is changed to the moving condition when the J-valued second motion judging result of at least one of adjacent pixels on the same line is judged to be the moving condition.
In the motion detection circuit, the first motion judging circuit includes a first peripheral pixel comparing circuit for detecting first polarities of the interframe difference luminance signal at each pixel at a first area around the target pixel and judging whether the image is moving in accordance with the detected first polarities with (J-1) threshold values to output a J-valued the first motion judging result. J is a natural number more than one. The second motion judging circuit may include a second peripheral pixel comparing circuit for detecting second polarities of the interframe difference signal at every other pixel in the horizontal and vertical directions at a second area around the target pixel and judging whether the image is moving in accordance with the detected second polarities with the (J-1) threshold values to output J-valued the second motion judging result. Moreover, the first motion judging circuit further includes a first polarity deviation detecting circuit for detecting third polarities of the interframe difference signal at each pixel of the video signal, detecting first agreement of the third polarities of all pixels at any of a first upper left area of the target pixel, a second upper right area of the target pixel, a first lower left area of the target pixel, and a first lower right area of the target pixel, and changing the first motion judging result from the first peripheral pixel comparing circuit from an intermediate moving condition to a moving condition in the presence of the first agreement when the first motion judging result from the peripheral pixel comparing circuit indicates the intermediate motion. The second motion judging circuit further includes a second polarity deviation detecting circuit for detecting fourth polarities of the interframe difference signal at each pixel of the video signal, detecting second agreement of the fourth polarities of every other pixels in the horizontal and vertical directions at any of a second upper left area of the target pixel, a second upper right area of the target pixel, a second lower left area of the target pixel, and a second lower right area of the target pixel, and changing the second motion judging result from the second peripheral pixel comparing circuit from an intermediate moving condition to a moving condition in the presence of the second agreement when the second motion judging result from the peripheral pixel comparing circuit indicates an intermediate moving condition.
The motion detection circuit may further include a majority detection circuit including a memory for detecting a majority of the judging results at Q pixels around the target pixels and judging the motion in the interframe difference signal at the target pixel in accordance with the detected majority to output the judging result such that the judging result is biased toward a moving condition when the judging results at Q pixels includes intermediate moving conditions. Q is a natural number more than one.
The first peripheral pixel comparing circuit may detect the first polarities among a positive polarity, a negative polarity, and a substantially zero level. The first peripheral pixel comparing circuit may include a comparing circuit for comparing the interframe difference luminance signal with a threshold value to detect the substantially zero level of the interframe difference luminance signal.
The second peripheral pixel comparing circuit detects the second polarities among a positive polarity, a negative polarities, and a substantially zero level. The second peripheral pixel comparing circuit includes a comparing circuit for comparing the interframe difference signal with a threshold value to detect the substantially zero level of the interframe difference signal.
The first polarity deviation detecting circuit detects the third polarities among a positive polarity, a negative polarity, and a substantially zero level. The first polarity deviation detecting circuit includes a comparing circuit for comparing the interframe difference luminance signal with a threshold value to detect the substantially zero level of the interframe difference luminance signal.
The second polarity deviation detecting circuit detects the fourth polarities among a positive polarity, a negative polarities, and a substantially zero level. The second polarity deviation detecting circuit includes a comparing circuit for comparing the interframe difference signal with a threshold value to detect the substantially zero level of the interframe difference signal.
The motion detection circuit may further include an edge detection signal generation circuit for detecting an edge at the target pixel in the video signal and detecting an edge at the pixel in the delayed video signal and outputting an edge detection signal from either of the detected edge in the video signal or the detected edge in the delayed video signal selected in accordance with a selection signal. Moreover, the first polarity deviation detecting circuit changes a size of the first upper left area, the second upper right area, the first lower left area, and the first lower right area in accordance with the edge detection signal. Moreover, the second polarity deviation detecting circuit changes a size of the second upper left area, the second upper right area, the second lower left area, and the second lower right area in accordance with the edge detection signal.
The motion detection circuit may further include an edge detection signal generation circuit for detecting an edge at the target pixel in the video signal and detecting an edge in the delayed video signal and outputting an edge detection signal from either of the detected edge in the video signal or the detected edge in the delayed video signal selected in accordance with a selection signal. Moreover, the majority detection circuit includes a switching circuit for outputting either of the motion judging result judged in accordance with the detected majority or the judging result from the third motion judging circuit in accordance with the edge detection signal.
According to this invention, there is provided a noise suppression apparatus. It includes: a motion detection circuit mentioned above; a circulation signal generation circuit including: a coefficient generation circuit for generating a coefficient k, kxe2x89xa60 less than 1 in accordance with the judging result of the motion detection circuit; and a multiplier for multiplying the video signal by the coefficient k to output a circulation signal; and a difference signal generation circuit for generating a difference signal between the circulation signal and the video signal to output a noise suppressed video signal.
In the noise suppression apparatus, the coefficient k generated when the motion judging circuit judges that the image is in a stopping condition is greater than the coefficient k generated when the motion judging circuit judges that the image is in a moving condition.